A conventional semiconductor apparatus, which is fabricated using a BGA (Ball Grid Array) technique, includes a board frame, a semiconductor device (chip) and a mold package. Herein, the term “board frame” means a frame type of board or substrate that is used for fabricating semiconductor apparatuses. The board frame may employ a copper-plated-lamination structure. The semiconductor device is mounted on an island of the board frame. The semiconductor device is electrically connected at electrodes to inner leads provided on the board frame using a wire-bonding technique.
The board frame is provided at the bottom surface with solder balls. The inner leads are connected to outer leads using wires or through holes.
For a resin molding process, two major techniques, potting and transfer molding, are used. Transfer molding has been increasingly used, because semiconductor apparatuses can be easily fabricated with low costs, and mass production can be easily realized. The board frame can be provided as an individual piece, or as a frame, on which a number of semiconductor devices are mounted together. Frame types of boards (or substrates) have been increasingly employed for fabricating a transfer-mold type of semiconductor apparatuses.
In fabrication, the board frame with the semiconductor device is set between molding dies (die set). Then the molding resin is injected into the cavity at a predetermined pressure. As a result, the molding package is formed and the semiconductor device is sealed.
In recent years, as electric devices have been miniaturized, it has been required to miniaturize a package for semiconductor device as well. In order to miniaturize such a package, for example, the distance between the outer edge of the mold package and the outer edge of the board frame is shortened. However, the board frame must be mechanically held with the molding dies. Therefore, it is difficult to shorten such a distance.
In Japanese Patent Laying Open No. H9-252065, a wiring board region, which includes an island a semiconductor device is to be mounted on, is pushed off (removed) from a board frame, then the pushed off (removed) region is pushed back to the original position. After a transfer molding process, the wiring board region, which has been pushed back, is taken out from the board frame.
According to the conventional technology, shown in Japanese Patent Laying Open No. H9-252065, the wiring board region with the semiconductor device may have a difference in level from the remaining frame region. The level difference is caused by the push-back processing. The level difference may be in a range between 10 μm and 20 μm. According to the conventional method for push-back process, the wiring board region tends to be higher in level than the remaining frame region.
As it is difficult to control the level difference between the wiring board region and the remaining frame region, the yield rate of semiconductor apparatuses is lowered. When the level difference occurs between the wiring board region and the remaining frame region, it is difficult to carry out a wire bonding process properly and completely. Further, in a transfer molding process, thin burrs are made easily around the wiring board region.
As the wiring board region is pushed-back, the wiring region may drop out from the board frame. Especially when the gate is removed after the transfer molding process, the wiring board region easily drops out from the board frame. Consequently, according to the conventional technology, it is difficult to miniaturize a semiconductor apparatus without lowering the yield rate.
In this application, the term “push back” means a process of removing a region once from the board frame, then soon returning it to the original position.